When I bought the car ( 2002 Acura RSX Type-S, 146k miles ), I noticed the engine light came on. I popped in an OBD2 and it read error codes P1298 and P0420. I could erase the P0420 code, but after a few miles it would come back on.

P1298: The official Honda definition for the P1298 error code is "High voltage ELD Circuit". This means that you are getting high input in the Electronic Load Detector. The Electronic Load Detector basically monitors how much current the charging system is using so it knows how much to charge the battery. Be sure to check for blown fuses first though, as it could be caused by a blown fuse from the wiring harness shorted on the underside of the intake manifold.

P0420: The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

For the P0420, I put Gumout fuel system cleaner, then the fuel injector cleaner for 2 fill-ups of premium. One I hit half a tank on the second fill I tried to reset the code again, success!

Now, the P1298. I went to an Acura dealer but they said I had to order the fuse box. I told him all I needed was the ELD, and he gave me a look. I said I had the parts number (thanks to akep on reddit for hunting it down! mass karma). He searched it, found it, not in stock. So he checked with the Honda down the road. I grabbed it there, also asked how much it would cost to run diagnostics on my car. It would come out to $110. So once I got home, I swapped the ELD with the new one no problems. I turned the car on, let it idle a bit, then popped in the OBD2 and said no problems. I tried to erase the DTU and still, everything was tip top. I went out for a few miles to see if running it would do anything, then testing. Nothing.

just to clarify do you mean your check engine light or maintenance required light? the maintenance required light comes on every ten thousand miles or so.there is a procedure in your owners manual to reset it and this youtube video http://www.youtube.com/watch?v=XI3t_wnv8iA. if its your check engine light then that has to be cleared with an obd2 scanner

just to clarify do you mean your check engine light or maintenance required light? the maintenance required light comes on every ten thousand miles or so.there is a procedure in your owners manual to reset it and this youtube video http://www.youtube.com/watch?v=XI3t_wnv8iA. if its your check engine light then that has to be cleared with an obd2 scanner

yeah that.

It sounds like you fixed your problem, as you have no CEL. I am somewhat skeptical about the P0420 staying off for long, but who knows.

As he said for the maintenance light its easy to turn off, but will be back in 10000 miles. In case you don't have the owners manual, the procedure is as follows:
1. Turn off the engine.
2. Press and hold the select/reset button in the instrument panel, then turn the ignition switch to ON (II).
3. Hold the button for about 10 seconds until the indicator goes off.

If you do have a manual and want to read what the page has to say, well that is a direct quote from it, but in my 2005 owners manual it is page 56.